A conventional technology of an electrically-driven hydraulic work machine such as a hydraulic excavator in which a hydraulic pump is driven by an electric motor to drive actuators to perform various works is disclosed in Patent Document 1 and Patent Document 2.
According to Patent Document 1, a configuration is proposed in which a hydraulic pump of fixed displacement type driven by an electric motor is provided and the rotational speed of the electric motor is controlled such that a differential pressure between a delivery pressure of the hydraulic pump and a maximum load pressure of a plurality of actuators is fixed to perform load sensing control. If this technology is used, then the number of hydraulic pipes can be decreased from that, in an alternative case in which the load sensing control is performed using a hydraulic pump of variable displacement type, and it is facilitated to apply high-efficiency load sensing control to a small-sized hydraulic excavator or the like in which the necessary installation space is small.
Meanwhile, according to Patent Document 2, an electrically-driven hydraulic work machine is proposed in which a hydraulic pump is configured as that of the variable displacement type including only a horsepower controlling function and a controlling algorism that simulates a horsepower control characteristic of a hydraulic pump of the variable displacement type is provided in a controller for controlling the rotational speed of an electric motor. If this technology is used, then a power storage device that is a power source for the electric motor can be made long-lasting and besides, the electric motor can be downsized in addition to the advantages of Patent Document 1.